US8981780B2 - Dipole locator using multiple measurement points - Google Patents
Dipole locator using multiple measurement points Download PDFInfo
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- US8981780B2 US8981780B2 US13/947,598 US201313947598A US8981780B2 US 8981780 B2 US8981780 B2 US 8981780B2 US 201313947598 A US201313947598 A US 201313947598A US 8981780 B2 US8981780 B2 US 8981780B2
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- 238000005259 measurement Methods 0.000 title description 8
- 238000000034 method Methods 0.000 claims description 28
- 230000000007 visual effect Effects 0.000 claims description 9
- 229910000859 α-Fe Inorganic materials 0.000 claims description 9
- 238000004804 winding Methods 0.000 abstract description 5
- 238000005553 drilling Methods 0.000 description 18
- 230000007704 transition Effects 0.000 description 12
- 230000005540 biological transmission Effects 0.000 description 7
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- 238000000429 assembly Methods 0.000 description 4
- 238000012937 correction Methods 0.000 description 4
- 238000013461 design Methods 0.000 description 4
- 238000012544 monitoring process Methods 0.000 description 4
- 230000008859 change Effects 0.000 description 3
- 238000010276 construction Methods 0.000 description 3
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- 230000010363 phase shift Effects 0.000 description 1
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Images
Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/15—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for use during transport, e.g. by a person, vehicle or boat
- G01V3/165—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation specially adapted for use during transport, e.g. by a person, vehicle or boat operating with magnetic or electric fields produced or modified by the object or by the detecting device
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- E21B47/02224—
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- E—FIXED CONSTRUCTIONS
- E21—EARTH OR ROCK DRILLING; MINING
- E21B—EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/02—Determining slope or direction
- E21B47/022—Determining slope or direction of the borehole, e.g. using geomagnetism
- E21B47/0228—Determining slope or direction of the borehole, e.g. using geomagnetism using electromagnetic energy or detectors therefor
- E21B47/0232—Determining slope or direction of the borehole, e.g. using geomagnetism using electromagnetic energy or detectors therefor at least one of the energy sources or one of the detectors being located on or above the ground surface
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
- G01V3/00—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation
- G01V3/08—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices
- G01V3/081—Electric or magnetic prospecting or detecting; Measuring magnetic field characteristics of the earth, e.g. declination, deviation operating with magnetic or electric fields produced or modified by objects or geological structures or by detecting devices the magnetic field is produced by the objects or geological structures
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q1/00—Details of, or arrangements associated with, antennas
- H01Q1/04—Adaptation for subterranean or subaqueous use
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q21/00—Antenna arrays or systems
- H01Q21/24—Combinations of antenna units polarised in different directions for transmitting or receiving circularly and elliptically polarised waves or waves linearly polarised in any direction
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q7/00—Loop antennas with a substantially uniform current distribution around the loop and having a directional radiation pattern in a plane perpendicular to the plane of the loop
Definitions
- the present invention relates generally to the field of locating underground objects, and in particular to locating and tracking a beacon within the field of operation of a horizontal drilling machine.
- the present invention is directed to a receiver system for identifying a location of a magnetic field source.
- the receiver system comprises a frame, a first antenna assembly supported by the frame, a second antenna assembly supported by the frame, and a processor.
- Each antenna assembly is adapted to detect the magnetic field from the source.
- the processor is adapted to receive an antenna signal from each of the antenna assemblies and to determine a location of the source relative to the frame using the antenna signals.
- the present invention is also directed to method for tracking a below ground source of a magnetic field.
- the method comprises simultaneously detecting in three dimensions a magnetic field from a source at each of at least two distinct points of a receiver frame.
- the method further comprises the step of determining a location of the source relative to the receiver frame using the detected field values.
- the present invention is further directed to a horizontal directional drilling system.
- the system comprises a drilling machine, a drill string, a downhole tool assembly and a receiver assembly.
- the drill string is operatively connected to the drilling machine.
- the downhole tool assembly is supported at a downhole end of the drill string and comprises a magnetic field transmitter.
- the receiver assembly comprises a frame, at least a first and second antenna assembly, and a processor.
- the first and second antenna assemblies are supported by the frame and adapted to detect a magnetic field from the magnetic field transmitter.
- the processor is adapted to receive an antenna signal from each of the antenna assemblies and to determine a location of the magnetic field transmitter relative to the frame using the antenna signals.
- the present invention includes a method for drilling a horizontal borehole.
- the method comprises placing a receiver assembly, comprising a plurality of antenna assemblies, on the ground in proximity of a drill bit, wherein each antenna assembly comprises triaxial antennas and aligning the receiver assembly with a desired bore path.
- the drill bit is advanced forward without rotation to perform a steering correction in the horizontal plane.
- An orientation of the drill bit relative to the receiver assembly and a distance of forward advance of the drill bit without rotation are transmitted from the receiver assembly to the operator.
- FIG. 1 is an illustration of a horizontal directional drilling system for drilling a horizontal borehole and a tracking system built in accordance with the present invention.
- FIG. 2 is a perspective view of a receiver assembly constructed in accordance with the present invention.
- FIG. 3 is a perspective, partially cut-away view of a support structure for an antenna assembly for use with the present invention.
- FIG. 4 is a perspective, partially cut-away view of the antenna assembly from FIG. 3 .
- FIG. 5 shows an alternative embodiment for an antenna assembly for use with the present invention.
- FIG. 6 is a block diagram of a portable area monitoring system constructed to detect and process signals emanating from a boring tool.
- FIG. 7 is a geometric representation of the relationship between the antenna arrangements of a receiver built in accordance with the present invention.
- FIG. 8 is a geometric representation of the relationship between a transmitter and the antenna arrangements of a receiver built in accordance with the present invention.
- FIG. 9 is representative visual display for a preferred embodiment of the present invention.
- FIG. 10 is a graphical representation of total magnetic field readings from a transmitter as detected by a receiver in the y-z plane.
- FIG. 11 is a graph showing the field readings of FIG. 9 in the y-z plane.
- FIG. 12 is an illustration of flux lines radiating from a transmitter, as depicted in the x-y plane.
- FIG. 13 is a geometrical representation of the relationship between a transmitter and a tilted receiver.
- the horizontal directional drilling (HDD) industry traditionally uses walk-over tracking techniques to follow the progress of a bore, to find the surface location immediately above the drill bit, and to determine the depth of the drill bit from that surface location.
- the primary tracking tools are a subsurface transmitter and a hand-carried surface receiver.
- the transmitter located in or very near a boring tool, generally emits a magnetic dipole field created by a single coil dipole antenna.
- the transmitted dipole field can be used for both location and communication with the above ground receiver.
- a receiver can locate a transmitter in the fore-aft direction (along the axis) using the amplitude and phase of the transmitter's generated horizontal and vertical field components as measured in the vertical plane normal to the surface and extending through the transmitter axis (the x-z plane).
- a receiver can also determine the location of a single transmitter in the left-right directions using the amplitude and phase of the dipole field in the horizontal plane (the y-z plane).
- FIG. 1 illustrates the usefulness of horizontal directional drilling by demonstrating that a borehole 12 can be made without disturbing an above-ground structure, namely a roadway or walkway as denoted by reference numeral 14 .
- a drill string 16 carrying a drill bit 18 is rotationally driven by a rotary drive system 20 .
- monitoring the position of the drill bit 18 is critical to accurate placement of the borehole and subsequently installed utilities.
- the present invention is directed to a system 22 and method for tracking and monitoring a downhole tool assembly 24 during a horizontal directional drilling operation.
- the HDD system 10 of the present invention is suitable for near-horizontal subsurface placement of utility services, for example under the roadway 14 , building, river, or other obstacle.
- the tracking system 22 for use with the HDD system 10 is particularly suited for providing an accurate three-dimensional locate of the downhole tool assembly 24 from any position above ground.
- the locating and monitoring operation with the present tracking system 22 is advantageous in that it may be accomplished in a single operation.
- the present invention also permits the position of the downhole tool assembly 24 to be monitored without requiring the tracking system 22 to be moved towards the transmitter 32 or to be placed directly over a transmitter in the downhole tool assembly.
- the HDD system 10 comprises the drilling machine 28 operatively connected by the drill string 16 to the downhole tool assembly 24 .
- the downhole tool assembly 24 preferably comprises the drill bit 18 or other directional boring tool, and an electronics package 30 .
- the electronics package 30 comprises a transmitter 32 for emitting a signal through the ground.
- the transmitter 32 comprises a dipole antenna that emits a magnetic dipole field.
- the electronics package 30 may also comprise a plurality of sensors 34 for detecting operational characteristics of the downhole tool assembly 24 and the drill bit 18 .
- the plurality of sensors 34 may generally comprise sensors such as a roll sensor to sense the roll position of the drill bit 18 , a pitch sensor to sense the pitch of the drill bit, a temperature sensor to sense the temperature in the electronics package 30 , and a voltage sensor to indicate battery status.
- the information detected by the plurality of sensors 34 is preferably communicated from the downhole tool assembly 24 on the signal transmitted by the transmitter 32 using modulation or other known techniques.
- the tracking system 22 comprises a receiver assembly 36 .
- the receiver assembly 36 comprises a frame 38 , a computer processor 40 , and a plurality of antenna arrangements 42 supported by the frame.
- the processor 40 is supported on the frame 38 and operatively connected to the plurality of antenna arrangements 42 .
- the frame 38 is preferably of lightweight construction and capable of being carried by an operator using a handle 44 .
- the receiver assembly 36 also comprises a visual display 46 and a battery 48 for providing power to the various parts of the receiver assembly.
- the visual display 46 may be adapted to provide a visual representation of the tracking system 22 relative to the drill bit 18 and other information useful to the operator.
- the receiver assembly 36 may also comprise a transmitting antenna (not shown) for transmitting information from the receiver assembly to the drilling machine 28 or other remote system (not shown).
- the antenna arrangements 42 are supported on the frame 38 and separated from each other by a known distance and in known relative positions.
- the separation and relative position of the antenna arrangements 42 may be selected based on the number of antenna arrangements and antenna design, size, and power.
- the plurality of antenna arrangements 42 comprises a first 42 a , a second 42 b , and a third 42 c antenna arrangement.
- the antenna arrangements 42 are mounted in a plane and at the vertexes of an equilateral triangle.
- a greater distance or spread between the antennas will provide better resolution and accuracy.
- a workable compromise between spread and physical size has been found to be a separation distance of at least 18 inches.
- each antenna arrangement 42 is capable of isolating the magnetic field in each of the Cartesian axes at the point on the frame 38 where the antenna is positioned.
- the invention contemplates a fourth antenna arrangement that may be supported by the frame 38 at position either above or below the plane formed by the first 42 a , second 42 b , and third 42 c antenna arrangements.
- Each of the plurality of antenna arrangements 42 is preferably a tri-axial antenna. More preferably, each antenna arrangement 42 is adapted to measure the total magnetic field at its respective position on the frame 38 . Preferably, each antenna arrangement 42 will comprise three orthogonal antennas which measure the magnetic field along their specific axis of sensitivity. Each of the three orthogonal antenna signals is squared, summed, and then the square root is taken to obtain the total field. This calculation assumes the sensitivities of each antenna are the same and that the center of each antenna is coincident with the other two such that the antenna arrangement is measuring the total field at a single point in space.
- the antenna arrangement 42 comprises a support structure 50 defining three channels 52 .
- the support structure 50 is preferably formed of lightweight plastic.
- the structure 50 may be manufactured in at least two parts that are secured together.
- the structure 50 is preferably manufactured in such a way that three channels 52 are each dimensionally identical. More preferably, the support structure 50 has a substantially cubical shape and each of the three channels 52 defines a rectangular aperture area having a center point. Most preferably, the channels 52 are mutually orthogonal and oriented so that the center points are coincident.
- the channels 52 are orthogonally oriented such that a first channel 52 a is circumvented by a second channel 52 b , and a third channel 52 c circumvents the first channel and the second channel.
- a preferred embodiment for such an arrangement comprises an orientation where a long side of the rectangular second channel 52 b is adjacent to and perpendicular to a short side of the rectangular first channel 52 a , and a diagonal of the rectangular third channel 52 c is substantially coincident with a plane formed by the rectangular second channel.
- the size of the antenna 42 can be optimized by designing the channels 52 such that the diagonal of the third channel 52 c intersects the plane of the second channel 52 b at an angle of between 0-10 degrees. Most preferably, the diagonal of the third channel 52 c will intersect the plane of the second channel 52 b at an angle of approximately 4 degrees.
- the antenna arrangement 42 further comprises three antenna coils 54 .
- the coils 54 are preferably insulated windings of magnet wire.
- the three coils 54 are separately wound around the structure 50 , one in each of the three channels 52 a , 52 b , and 52 c , to form three coil loops 54 a , 54 b , and 54 c . Because of the orientation of the channels 52 a , 52 b , and 52 c , as previously described, the coils 54 a , 54 b , and 54 c do not intersect each other when positioned in the channels.
- the coils 54 comprise approximately 100 turns of magnet wire, though other numbers of turns may be used depending on wire size and antenna sensitivity or other design considerations.
- the coil loops 54 all have coincident center points, and their sensitivities are substantially identical.
- the coil loops 54 also define substantially identical aperture areas and have rounded corners. Since the coils 54 are wound with magnet wire, their resistances are relatively low. Therefore, the antenna 42 can be tuned properly to increase its sensitivity, thus allowing the receiver 36 to detect the magnetic field from greater depths.
- the antenna arrangement 42 also contemplates other embodiments for the antenna arrangement 42 , including use of traditional ferrite rod antennas.
- the antenna arrangement 42 could comprise three ferrite rod antennas in orthogonal relationship.
- the antenna arrangement 42 having coil windings 54 shown in FIG. 4 has significant advantages over the use of traditional ferrite rod antennas. Ferrite rods greatly enhance the sensitivity of the antenna, thus enabling the receiver to work to deeper depths. However, the ferrite properties are not constant over a temperature range. If a high level of accuracy is required, the drift over the temperature range experienced on work sites is unacceptable. Also, the center of each antenna would obviously not be coincident with the center of the other antennas. This will introduce errors in the total field calculation.
- the antenna arrangement 55 comprises three tri-axial antennas made of printed circuit boards 56 (PCBs).
- the PCBs 56 are supported on a mount 58 and configured as a cube. In a cubic configuration, opposite PCBs 56 are connected in series.
- the PCBs 56 are preferably comprised of many connected layers, allowing the winds to be connected in series to increase the number of turns, and therefore the inductance of the antennas.
- the PCBs 56 antennas can be mounted such that their respective axes are perpendicular and a geometric center of the antenna arrangement 55 will not change as the antenna arrangement is maneuvered.
- PCBs 56 for the antenna arrangement 55 also has significant advantages.
- the cubic arrangement of the PCBs 56 allows the observation point for calculation of the total field sensed by the antenna arrangement 55 to remain at the geometric center of the antenna. Additionally, as PCBs are manufactured by precision machines, tolerances associated with manually wrapping the loops are reduced. The antennas produced in this fashion are very uniform from one board to the next and less expensive to manufacture. Higher precision measurements will be possible with this configuration.
- FIG. 6 shown therein is a block diagram of the preferred embodiment of the receiver assembly 36 of the present invention.
- the antenna arrangements 42 as described earlier, measure a change in the magnetic field. A change in the magnetic field sensed will result in a voltage being induced in response to the transmitter's magnetic field.
- the voltages from the antennas 42 are sent to filters 60 and amplifiers 62 . Filters 60 eliminate the effects of other signals received by the antennas 42 from local noise sources. Amplifiers 62 increase the signal received by the antennas 42 .
- An A/D converter 64 is used to convert analog waveform information into digital data.
- the digital data from the A/D converter 64 is then sent to a central processor 66 (CPU) to calculate the location of the transmitter 32 relative to the receiver assembly 36 .
- the CPU 66 may comprise a digital signal processor (DSP) and a microcontroller.
- DSP digital signal processor
- the CPU 66 decodes the information from the A/D converter 64 and performs calculations to determine the location of the transmitter in a manner yet to be described.
- the CPU 66 may also discern information transmitted on the magnetic field, to determine the battery status, pitch, roll, and other information about the downhole tool assembly 24 .
- the receiver assembly 36 may also comprise one or more sensors 68 used to sense operational information about the receiver assembly 36 .
- sensors 68 used to sense operational information about the receiver assembly 36 .
- one or more accelerometers, or other known inclination and orientation sensors or magnetic compasses may provide information concerning the roll or tilt of the receiver 36 .
- Information from the sensors 68 is provided to the A/D converter 64 and to the CPU 66 where the DSP may make calculations to compensate for the receiver 36 not being level.
- the receiver 36 is preferably powered by a battery assembly 76 and power regulation system 78 .
- the battery assembly 76 may comprise multiple D-cell sized batteries, though other sources are contemplated, such as rechargeable batteries.
- the power regulation system 78 may comprise a linear regulator or switch mode regulator to provide power to the various components of the receiver 36 .
- the receiver assembly 36 of the present invention uses multiple points of measurement, at the plurality of antenna arrangements 42 , to accurately locate the transmitter 32 in three-dimensional (3-D) space.
- Each antenna arrangement 42 obtains three distinguishable orthogonal components of a magnetic field available at any position.
- the three antennas 42 a , 42 b , and 42 c provide those magnetic field measurements.
- the present invention can therefore be used to identify the exact coordinates of the receiver 36 relative to the transmitter 32 using the magnetic field measurements from the plurality of antenna arrangements 42 and the equations above.
- the present invention can be used to identify the location of the transmitter 32 in 3-D space without any additional movements, as long as the magnetic field from the transmitter can be detected by the plurality of antenna arrangements 42 .
- the location of the transmitter 32 can be determined without movement of the receiver 36 towards the transmitter 32 .
- the information concerning the location of the transmitter 32 is preferably provided to the operator using the visual display 72 .
- FIG. 9 There is shown in FIG. 9 a preferred configuration of a screen display 72 .
- the drill string 16 is shown underground.
- the x-, y-, and z-coordinates are the distances to the downhole tool assembly 24 from the receiver 36 location.
- a receiver icon is also on the grid to graphically show the relationship of the receiver 36 to the transmitter 31 .
- Transmitter 32 temperature, battery status, pitch, roll, yaw, signal strength, signal gain, and signal frequency icons are also shown on the display 72 to provide a graphic and numeric representation of each.
- Other downhole tool 18 data or operational information could similarly be displayed. This allows the downhole tool assembly 24 position to be monitored and determined without requiring the receiver 36 to be placed directly over the transmitter 32 . All data may be stored in memory or a database to log the history of each bore. Many other functions may be made available thru the main menu such as changing units, calibration mode, alternate two-dimensional view, and demonstrations and help.
- the receiver assembly 36 of the present invention can also be used with certain directed steps to take advantage of situations where the transmitter 32 strength or sensitivity of the plurality of antenna arrangements 42 does not permit the 3-D location as described above.
- use of the receiver assembly 36 involves location of a particular spot directly behind the transmitter 32 before pinpointing the location of the transmitter.
- the receiver can easily direct an operator to the proper spots to ease determination of the location of the transmitter.
- the alternative use involves a process of using the visual display 72 to first direct the operator to a position directly behind and oriented in the same direction as the downhole tool assembly 24 and then to a position directly above the downhole tool assembly.
- V 1 - 2 r _ 1 - r _ 2 L
- V 1 - 3 r _ 1 - r _ 3 L
- V 2 - 3 r _ 2 - r _ 3 L
- V y V 1-2
- V z V 2 - 3 ⁇ cos ⁇ ⁇ 6 + V 1 - 3 ⁇ cos ⁇ ⁇ 6 .
- the display 72 can be used to direct the operator to rotate the receiver assembly 36 so that the receiver is directionally aligned with the transmitter 32 and, consequently, the downhole tool assembly 24 .
- the receiver assembly 36 will be aligned with the transmitter 32 when the flux line through the antenna assembly 42 c at the back end of the receiver (the “rear pod”) is along the z-axis.
- the display 72 By using the display 72 to show the operator the angle at which the flux impinges the rear pod 42 c , the user can align the receiver 36 with the flux lines and keep it rotated properly.
- the next step in the process is to direct the operator to move the receiver 36 to a position directly above the transmitter 32 to precisely locate the downhole tool assembly 24 .
- trackers and beacons used for directional drilling generally do not indicate how much the drill bit is moving as an HDD system 10 is used to make steering corrections to redirect the borehole 12 .
- steering corrections are dependent on machine operators' expertise.
- the present invention removes the uncertainty of operators' guesswork.
- the receiver 36 can indicate at any given point in time the precise relative location of the downhole tool assembly 24 and the drilling bit 18 .
- the receiver 36 can be set on the ground with a centerline of the receiver directly on the desired path for the borehole 12 .
- the display 72 can then be used to provide the operator with immediate feedback of the location and heading of the drill bit 18 relative to the desired path.
- a method for creating a horizontal directional borehole 12 in the earth is also accomplished with the following steps.
- the receiver assembly 36 is placed on the ground in the proximity of the drill bit 18 with the longitudinal display axis of the receiver assembly aligned with the desired bore path 12 .
- an image of the orientation of the drill bit relative to the receiver 36 can be transmitted from the receiver to the HDD system 10 and its operator.
- the distance of forward advance of the drill bit 18 without rotation can be determined at the receiver 36 and that information also transmitted from the receiver to the FIDD system 10 .
- Such techniques are useful when boring on-grade boreholes or when desiring to bore to a point where the receiver 36 is positioned.
- the present invention contemplates an adaptation of a data transmission technique known as Manchester coding.
- Other data transmission variants may have similar characteristics.
- the invention will be described in terms of Manchester coding, the invention may be used with any data transmission technique meeting similar data signal criteria.
- Biphase-L (-Level), in which a “1” or “0” is represented by a level transition in the middle of the bit interval.
- Biphase-L is commonly known as Manchester or Manchester II code.
- Manchester II or Biphase-L code occasionally is further subdivided into Bipolar One (logic “0” is defined as a low-to-high or rising edge transition in the middle of the bit period, or Bipolar Zero (a logic “0” is defined as a high-to-low or falling transition in the middle of the bit period.
- Manchester/FSK coding provides no power savings relative to FSK or PSK transmission, but it does provide greater operational flexibility.
- This arrangement presumes one or more digital bandpass filters, each identified by different filter coefficients, and the ability to generate a number of different FSK waveforms, also determined by coefficients in software.
- the bandpass filter response will produce an output very similar to Manchester/OOK coding as the FSK signal moves in and out of the bandpass filter passhand.
- the operator may select the operating frequency from a number of different frequency and filter combinations to obtain the combination offering the best overall performance in the presence of local noise or other interference.
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- Electromagnetism (AREA)
- Environmental & Geological Engineering (AREA)
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Abstract
Description
where r2=x2+y2+z2, and k is a calibration constant. These equations assume that the
Also, it can be seen from
or z1=r1·cos θ1. The same is true for the other points, so in general zi=ri·cos θi.
z′=z cos P+x sin P x′=−z sin P+x cos P
Plugging in the rotated values and simplifying gives:
Then
And then Vy=V1-2 and
These vectors can be shown in two-dimensional (2-D) space to direct the operator to the spot where the vectors are 0, where B1T=B2T=B3T.
Since me
-
- NRZ-L (-Level), in which a high level represents a “1” and a low level represents a “0”,
- NRZ-M (-Mark), in which a “1” is represented by a transition and a “0” by no transition in the bit period,
- NRZ-S (-Space), in which a “0” is represented by a transition and a “1” by no transition in the bit period.
NRZ-L is seen to be the most common (and intuitive) of the data codes.
-
- (1) by tuning the beacon transmitter on or off to represent a signal condition (the “1” state) and a no signal condition (the “0” state), respectively, or
- (2) by frequency shifting the beacon transmitter frequency in or out of a bandpass filter passband to represent the “1” and “0” states, respectively. In other words, the in-band signal frequency is generated during the high portion of the Manchester waveform and an out-of-band signal frequency is generated during the low portion of the Manchester waveform.
For simplicity, let alternative (1) be called Manchester/OOK (Manchester On-Off Keying) and let alternative (2) be called Manchester/FSK (Manchester Frequency Shift Keying).
Claims (18)
Priority Applications (1)
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US13/947,598 US8981780B2 (en) | 2005-05-13 | 2013-07-22 | Dipole locator using multiple measurement points |
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US68078005P | 2005-05-13 | 2005-05-13 | |
US72806605P | 2005-10-19 | 2005-10-19 | |
US11/382,644 US7786731B2 (en) | 2005-05-13 | 2006-05-10 | Dipole locator using multiple measurement points |
US12/844,886 US8497684B2 (en) | 2005-05-13 | 2010-07-28 | Dipole locator using multiple measurement points |
US13/947,598 US8981780B2 (en) | 2005-05-13 | 2013-07-22 | Dipole locator using multiple measurement points |
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US12/844,886 Continuation US8497684B2 (en) | 2005-05-13 | 2010-07-28 | Dipole locator using multiple measurement points |
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US12/844,886 Active 2026-05-12 US8497684B2 (en) | 2005-05-13 | 2010-07-28 | Dipole locator using multiple measurement points |
US13/947,598 Active 2026-06-01 US8981780B2 (en) | 2005-05-13 | 2013-07-22 | Dipole locator using multiple measurement points |
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Also Published As
Publication number | Publication date |
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US20100289496A1 (en) | 2010-11-18 |
US7786731B2 (en) | 2010-08-31 |
WO2006124520A3 (en) | 2007-05-03 |
GB2439495A (en) | 2007-12-27 |
US20060254820A1 (en) | 2006-11-16 |
US20130307544A1 (en) | 2013-11-21 |
US8497684B2 (en) | 2013-07-30 |
WO2006124520A2 (en) | 2006-11-23 |
GB2439495B (en) | 2010-09-22 |
GB0718922D0 (en) | 2007-11-07 |
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